Puncture test

Examination of oven-aged samples has demonstrated that substantial degradation is limited to the outer surface (34), ie, the oxidation process is diffusion limited. Consistent with this conclusion is the observation that oxidation rates are dependent on sample thickness (32). Impact property measurements by high speed puncture tests have shown that the critical thickness of the degraded layer at which surface fracture changes from ductile to brittle is about 0.2 mm. Removal of the degraded layer restores ductiHty (34). Effects of embrittled surface thickness on impact have been studied using ABS coated with styrene—acrylonitrile copolymer (35). 

Various tests may be used to determine the survivability of unexposed polymeric GMs. Puncture tests are frequently used to estimate the survivability of FMLs in the held. During a puncture test, a 5/16 steel rod with rounded edges is pushed down through the membrane. A very hexible membrane that has a high strain capacity under biaxial tension may allow that rod to penetrate almost to... 

Figure 8,10 illustrates the general configuration for testing a film s puncture resistance. We can perform this test in a number of ways. The probe may be attached to the crosshead of a universal testing machine, similar to the one illustrated in Fig. 8.3. We drive the probe down through the film at a constant speed, while recording the force. Alternatively, we can perform an impact puncture test, in a similar fashion to impact plaque testing.

Figure 8.10 Schematic illustration of film puncture testing...

Figure 8.11 Effect of orientation on deformation zones observed during puncture testing, viewed from above ...

ISO 7765-2, Plastics film and sheeting - Determination of impact resistance by the free-falling dart method - Part 2 Instrumented puncture test, 1994. 

The yield force reading obtained from a puncture test was found to depend on the perimeter and area of the punch (Bourne, 1979), as illustrated in the equation (Bourne, 1982) ... 

Bourne, M.C. 1979. Theory and application of the puncture test in food texture measurement. In Food Texture and Rheology (P. Sherman, ed.) pp. 95-142. Academic Press, New York. 

Figure 8-25 Compression and Shear Components in Penetration Tests. Source From M.C. Bourne, Measure of Shear and Compression Components of Puncture Tests, J. Food Sci., Vol. 31, pp. 282-291, 1966.

Bourne, M.C. 1966. Measure of shear and compression components of puncture tests. J. Food Sci. 31 282-291. 

In order to find the amount of plasticiser which ensured proper ion-selective electrode function and optimised mechanical properties, puncture tests were used to evaluate the effects of changes in plasticiser levels and... 

Fig. 15 Evolution of the plastic energy, Gpiast) of a non-nudeated and of a -nucleated PP in between - 60 and 120 °C a puncture tests, b Charpy tests. Tests performed on injection molded specimens...

Behcet s disease (+) HLA-B5 or (-) BW51 — Internist, rheumatologist Behget s skin puncture test... 

Polymer embrittlement was determined by 180° fold and/or pencil puncture tests. Elongation in the transverse direction of the LDPE samples was measured on an Instron TT-C tensile tester at 70°F and 65 relative humidity. The time to break was 25-50 sec. for 2 mm strips utilizing a gauge length of 0.5" and jaw-type clamps. 

The puncture test was realized as described previously by Gontard et al. (1992). To avoid any thickness variation, the puncture strength values were divided by the thickness of the film. Three replicates of each film type were tested. 

Moisture content was determined by drying them under vacuum to constant weight at 60°C (AOAC, 1980). Water activity was measured at 25°C by using a Decagon Cx-3 (Aqualab) hygrometer. Mechanical properties of dried samples with different water content were analyzed at 30°C by using a puncture test with a Universal Texture Analyser (TA.XT2, Stable Micro Systems). A cylindrical 2.0 mm diameter pimch was used at a penetration rate of 1.5 mm/sec until total sample penetration. Determinations were made in five different samples with the same water content. 

Throughout a puncture test, mechanical properties of samples with different moisture content were analyzed. Parameters obtained from these curves were the maximum force required to break the sample (Fmax)/ distance at this point (d) and the ratio force-distance at the break point. The ratio force-distance at the break point (Fmax/rf) is related to the product resistance to fracture or sample firmness (Prothon et al., 2001). The ratio Fmax/d has been represented vs. the moisture content in Figure 63.3, showing a sigmoid relationship, also typical in crispy products (Peleg, 1994). This behavior indicates a decrease from the resistance to deformation with the increment in moisture product content, as a consequence of the plasticizing effect of water. The ratio was adjusted to the Fermi s model... 

The primary textural property of fruits and vegetables is firmness (6). Three principles are used to measure firmness. 1) The puncture test measures the force required to push a probe into the product. 2) The extrusion test measures the force required to make the product flow through one or more slots or holes. 3) The deformation test measures the distance the product compresses under a small force. All three test principles are used on fresh produce, but only the first two (puncture and extrusion) are used on processed material (7). 

An example of this approach is shown with carrots (19). Seventeen cultivars of carrots were sliced transversely and blanched 4 min at 212F or 165F, then canned and processed 23, 30,45,60,75 min at 250F. The firmness of the phloem tissue and xylem tissue (core) were separately measured by a puncture test. Figure 5 shows log firmness versus process time for the cultivar Dominator Sunseed together with the equations for the lines of best fit and the correlation coefficients R. Similar plots were obtained for the other sixteen cultivars. Sufficient data was obtained to measure substrate "b" and the thermal firmness value. No data were collected to measure substrate "a" because it is not needed. However, the firmness at zero process time was measured and these points are plotted on the ordinate. The correlation coefficients range from r = 0.98 to r = 1.00 which shows the excellent fit of the empirical data to the kinetic model. 

High speed puncture test ASTM D3763. 

ISO 7765-2 1994. Plastics Film and Sheeting - Determination of Impact Resistance by the Free-Falling Dart Method - Part 2 Instrumented Puncture Test. 

Cutting or puncture tests are. as mentioned previously, normally made with geometries intended to simulate service conditions. 

Conventional tensile and tear tests are not particularly suitable tools for a detailed investigation of strength-related properties of. small finished components or over the thickness of a bulky product, unless the item can be sectioned to size. An alternative approach, particularly suitable for diagnostic work, involves the use of a puncture test [17]. An indentor of specified geometry is pressed into the component, and the force to cause rupture is measured at a specified penetration or over a range of depths. One suitable application is the study of aging across the thickness of a bulky product [18]. 

ISO 6603-2, Determination of multiaxial impact behaviour of rigid plastics Part 2 Instrumented puncture test, 1989. 

BS 2782, Method 353B, Determination of multiaxial impact behaviour by the instrumented puncture test. 1991. 

---